Midterm 1 Review Flashcards
over the course of brewing, what happens to the specific gravity?
makes a descending hill shape, much like what i’d like to sled down (dashed line)
decreases because density density of sugar is greater than EtOH, and sugar is being converted to EtOH
over the course of brewing, what happens to the fusel alcohol content?
it increases because saccharomyces will always make it, just in lower concentrations than etoh. eventually the curve levels off when sugar is depleted.
over the course of brewing, what happens to the temperature?
the temperature increases then decreases due. the respiration of the growing yeast causes the increase and then the temperature needs to be cooled to 20-22C otherwise more fusel alcohols will be produced.
over the course of brewing, what happens to pH?
pH decreases to about 4ish due to the consumption of free amino nitrogen and conversion to organic acids and excreted protons. a bit too steep for me to want to sled down :0
over the course of brewing, what happens to ester content?
it increases due to the esterification of ethanol; mirrors the production of alchol
AAB can have a _____ growth curve
diauxic
why do some AAB exhibit a diauxic growth curve?
the original log phase is due to oxidation ethanol to acetic acid. these AABs can oxidize acetic acid via TCA cycle, which is responsible for the second growth phase.
if the starting concentration of ethanol is above ___%, the diauxic growth curve does not occur because _____ _____ concentration is too high.
3%; acetic acid
too much acetic acid kills cells
what are some multi-organism fermentations?
- sake
- fukuyama pot vinegar
- kefir
what is the role of koji in production of pot vinegar?
converts starch to sugars for LAB and yeast to metabolize first, then they die off when AAB become more prominent at the surface
why are pectinolytic microbes required during coffee fermentation?
enables removal of cherry from the bean
why is komagataeibacter sp and not acetobacter used in industrial vinegar
koma is better capable of handling the higher concentrations of acetic acid >15%
why are LAB and not AAB used for dairy fermentations
our primary fermentable sugar is lactose
what type of organism is used for rind formation on surface ripened cheese? LAB, AAB, or mold?
mold
Most yogurt cultures have approximately equal numbers of what two organisms?
streptococcus thermophilus and lactococcus bulgarius
what is the common species succession in vegetable fermentation?
1) leuconostoc
2) lactobacillus plantarum
3) lactobacillus brevis
why are coffee beans fermented?
to remove coffee cherry
why are cocoa beans fermented?
to remove pulp, develop flavors, reduce bitterness, and BEAN DEATH
why are campden crush tablets added to wine must?
kills AAB and natural flora, dechlorinates and acts as an antioxidant
why are coffee beans fermented?
to remove coffee cherry/mucilaginous pulp
why are campden crush tablets added to wine must?
kills AAB and natural flora, dechlorinates and acts as an antioxidant
why is an air lock required when making wine?
provide anaerobic environment; protect against AAB; yeasts are more efficient with alcohol production in anaerobic environment
why are needles used to puncture blue cheese during ripening process?
molds on the inside need to exchange gas to grow
why is bean death important to the chocolate making process
if beans are alive, they’ll undesirably utilize the fermentable sugars
why are hops added?
flavor development
why is yogurt fermentation generally carried out at 42C?
Streptococcus thermophilus and lactobacillus bulgaricus have different optimal temps. 42 is a compromise between the two.
why is citric acid in milk important for the flavor development in cheese?
citric acid can be converted to acetaldehyde and diacetyl aka the desired flavors
why is lactic acid fermentation sometimes required for finishing wine?
(malo) lactic fermentation imparts a buttery flavor. Oenococcus oeni
ex) chardonnay
what is the role of rennet in cheese production?
enables curding
what roles does casein have in the textural development of cheese curds?
caseins make up 80% of milk’s proteins. cheese is made by the coagulation of casein, which happens when they are converted to a nonpolar form to separate from water and entrap fat and minerals in the process. the more fat that is trapped, the stronger the curd.
the casein matrix influences the cheese’s ability to expel whey.
what roles does casein have in the textural development of cheese curds?
interaction of between acid destabilized k-casein and denatured whey
what does L. bulgaricus produce for S. thermophilus in yogurt fermentations?
peptides/amino acids
what biochemical is the most important contributor to taste in yogurt?
acetaldehyde
what is Nata de Coco composed of?
cellulose made by AAB on the surface of coconut water
what’s special about civit coffee?
it’s an intestinal fermentation
in the 1980s, what was special about activia yogurt?
has probiotic (bifidobacteria)
what are some differences between commercially sold sauerkraut and the sauerkraut you produced as part of this class?
commercial: - sold hermetically sealed and sterile - pasteurization partially cooks and softens - adds wine and spices Ours: - crunchier
is sugar added to grape must prior to wine fermentation?
nope
are all store-bought pickles fermented?
no
what types of olives are treated with lye prior to fermentation?
green
what’s the difference between pH and titratable acid
note: organic food acids tend to be partially ionized, unlike strong acids
titratable acid (aka total acidity): measures the total acid concentration in a food
pH is the measure of H+ present
why do gram-negative bacteria tend to die during the first few days of LAB mediated fermentation reactions?
LA can diffuse in more easily inside the cell where it dissociates and kills
why do bacteriophages cause more of a problem for dairy fermentation than veggie ferments?
- dairy relies more heavily on a single strain while veggie relies on many. a bacteriophage can cause a dead vat with dairy, which is less likely to happen with vegetables due to the backup strains.
why is it important to start an AAB fermentation to produce vinegar with a starting ethanol concentration above 3%?
avoid overoxidation
how to AA resist being killed by acetic acid?
overoxidation, acetic acid pumps, general stress proteins, decreased surface area for lipophilic passive transport
if white mold forms on the surface of your wine, what should you do?
throw it out
what media do you use to differentiate homo/heterofermentative LAB?
HHD
what is a great media for isolating Listeria from mixed microbial communities?
PALCAM
what type of media is used to support the growth of lactobacilli?
ADPA, MRS
What is OGYE media used for
yeast
SCOBY = ?
symbiotic culture of bacteria and yeast
HHD = ?
hetero and homo differentiation
AAB = ?
acetic acid bacteria
what’s the purpose of a Woronin body?
a) block septum between hyphae to keep damage from spreading to additional cells
b) act as a spore that is produced asexually by A. oryzae fungi
c) promote fungal growth by activating tip extension
d) participate in cyclic secretion of amylases
e) critical for sustaining high levels of amylases from A. oryzae
a
an example of a traditional fermentation product that relies on a mix of yeast, mold, LAB and AAB is a) Kefir b) Kombucha c) Sake D) Fukuyama pot vinegar E) Camembert cheese
d
a beer that has undergone a very low apparent attenuation will taste:
a) dry
b) dark
c) sweet
d) slightly acidic
e) like hops
c
is applying consistent moisture to hope necessary?
no
CO2 is more soluble at (higher/lower) temperatures
lower
sulfur dioxide is not:
a) widely used in the food industry
b) able to rapidly dissociate into bisulfite and sulfite in cells
c) able to inhibit the growth of microorganisms
d) able to degrade the cellular membrane of AAB
e) able to rapidly kill wild yeast
d
both heterofermentative and homofermentative LAB can produce diacetyl (true or false)
true
AAB results in the oxidation of EtOH to acetic acid, producing odors and off flavors for wine
true
why do you add a single campden crush tablet to your wine preparation?
kill off wild yeast, dechlorinate, and act as an antioxidant
name 2 fermented products that make use of an airlock
sauerkraut, wine, cider
LAB are used in dairy fermentations because they are very proteolytic. from the perspective of LAB, why is proteolysis essential to their survival and proliferation?
lack systems to produce their own amino acids so they must obtain them externally. their enzymes enable the breakdown of many proteins, providing a wider range of amino acids available to them
why is C. botulinum not a concern in your sauerkraut production?
salt content + acidity from LAB
define selective media
allow certain types of organisms to grow, and inhibit the growth of other organisms.
define back slopping
adding in a portion of a previously successful fermentation to start a new one
define surface static process
AAB fermentation; forms cellulose raft on surface to maintain access to O2.
define nata de coco
made from komagataeibacter (AAB) on the surface of coconut water
define homofermentative lactic acid bacteria
produce 2 mol of lactic acid per mole of glucose via glycolysis
define gravity (as applied to alcohol fermentations)
specific gravity is the gravity relative to water. used to monitor the fermentation as the breakdown of sugars into ethanol results in a lower SG
define coagulation
the disruption of micelle structure in milk to cause protein insolubility and aggregation, forming clumps
define kefir
dairy fermented drink made with yeast and LAB
attenuation
measure of how complete the alcohol ferment is (beer); lower attenuation = less alcohol but more sugar
overoxidation
ability for AAB to oxidize acetic acid using the TCA cycle. may also occur with other organic acids
what’s koji?
Aspergillus oryzae; mold; used in sake production
why is koji the mold of choice for any fermentation that requires the breakdown of starch. name one fermented food product that requires koji for its production
- most microbes can’t make use of starch
- koji has amylases to break down starch into simpler sugars
- has a variety of enzymes to attack a variety of bonds, widening the range of starches that can be used as substrate
- sake: used to break down rice, then LAB & yeast grow to outcompete spoilage microbes. the yeast produces alcohol
- koji doesn’t coexist with yeast and LAB
are LAB amino acid auxotrophs?
yeah
the most common type of microorganism that participates in the fermentation that produces kimchi is:
LAB
the most common organism that participates in the fermentation that produces wine is:
yeEEEEEeeeast
the microorganism that breaks down sugars during the production of sake is
mold
the microorganism that is responsible for rind formation on the surface of ripened cheeses is
mold
globally, most vinegar is produced by _____ sp. using an oxidative fermentation reaction
a) acetobacter
b) gluconobacter
c) gluconacetobacter
d) komagataeibacter
d
Where can you get a potentially novel acetic acid bacteria?
a) surface of grape
b) commercial bottle of traditionally fermented vinegar
c) soil
d) wine bottling facility
a
ethanol is converted into what during oxidative fermentation, before being converted to acetic acid?
acetaldehyde
heterofermentative bacteria
a) produce 2 moles of lactate for every one mole of glucose
b) use the 6-PG/PK pathway to ferment glucose
c) produce 2 ATP molecules for every one molecule of glucose
d) use glycolysis to ferment glucose
b
an ascus has greater resistance to environmental conditions than stationary phase cells
true
an ascus has greater resistance to environmental conditions than stationary phase cells
true
of these, which are aerobic and anaerobic? AAB, LAB, yeast, mold
aerobic: mold and AAB
anaerobic: LAB and yeastr
